Sugar or sugar-alcohol fatty acid esters such as sucrose fatty acid esters find uses in food industry as a nonionic surfactant. These esters have been conventionally synthesized by the transesterification of lower alkyl esters of fatty acids with sugars or sugar alcohols.
Several methods are known to produce sugar esters in a industrial scale. In a process generally known as the "solvent process", the fatty acid ester is reacted with sugar in a solvent such as dimethylformamide or dimethylsulfoxide in the presence of a basic transesterification catalyst. Another process known as the "microemulsion process" comprises the steps of dispersing the fatty acid ester in a solution of sugar in a solvent such as propylene glycol or water with the aid of an emulsifier such as soap and then removing the solvent before the transesterification takes place. A further process known as the "direct process" comprises reacting the fatty acid ester, the sugar and the basic transesterification catalyst in a molten mixture.
These known methods commonly require a high reaction temperature and thus the resulting products tend to color or darken with caramelized sugar. When dimethylformamide or dimethylsulfoxide is used, it makes the product unacceptable as a food additive.
It is a principal object of the present invention to provide a novel method for synthesizing sugar or sugar-alcohol esters of higher fatty acids which obviates the above-described disadvantages.
Other objects and advantages will become apparent as the description proceeds.